the.com/insincerity

means Speech or behavior that doesn't match what the person actually feels or believes — words performed rather than meant.

from From Latin sincerus, meaning 'clean' or 'whole' — possibly from a root tied to one-growth purity, like honey untainted by wax, or wine without added water. Add the negating 'in-' and you get something adulterated: a mixture, a cut product, feeling diluted with performance. The popular story that sincerus comes from 'sine cera' (without wax) — as in unblemished marble statues — is a charming Latin-class legend, not established etymology.